The invention relates to a coupling hook, especially for the lower steering arms of a three point attaching device of a tractor. The coupling hook has a hook member and a locking catch which is pressurized towards the locking position by a closing spring and which may be moved into the open position by means to be connected thereto. The hook member includes a bearing recess which is open on one side and intended to be attached to the bearing ball of an implement. The coupling hook also includes a recess to accommodate the locking catch and an aperture to allow part of the locking catch to pass into the region of the bearing recess. A first stop face is provided by the aperture face above the locking catch and is arranged towards the open end of the bearing recess. A second supporting stop is arranged at a distance from the first stop face. Further included is means for securing the locking catch in the locking position. The locking catch, on its upper side, includes a first supporting face which cooperates with the first stop face. The two faces contact one another in the locking position in a contact point. On its underside, the locking catch includes a second supporting face cooperating with the second supporting stop, and means cooperating with the means for securing the locking catch in its locking position. Furthermore, at its front end, the locking catch engages the bearing recess, and includes the locking catch, an unlocking face, a stop for limiting the adjusting movement of the locking catch and a locking face for arresting the bearing ball in the bearing recess.
A coupling hook is described in DE 26 18 332 C2 which corresponds to U.S. Pat. No. 4,108,464. This reference illustrates a coupling hook where part of the locking catch is guided outwardly from a through-aperture and to which a cable is attached for actuating the locking catch. However, the locking catch is designed and supported relative to the locking stop in such a way that, if, under operational conditions, the locking catch is subjected to any kind of influences, for instance resulting from the bearing pin or branches or the like, it may open.